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BULLETIN OF THE 



No. 168 




Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief. W 
July 15, 1915. 



GRADES FOE COMMERCIAL CORN. 

ByjlwfT/DuvEL, 
Crop Technologist in Charge of Grain-Standardization Investigations. 

CLASSIFICATION OF CORN. 

By virtue of the authority vested in the Secretary of Agriculture 
by the acts of Congress of June 30, 1906 (34 Stat., 669), and of 
March 4, 1913 (37 Stat., 828), to fix definite grades of grain, the grades 
for corn shown in Table I were fixed and promulgated on January 
3, 1914, to take effect on July 1, 1914. 

Table I. — Grade classification of white, yellow, and mixed corn, showing maximum 
allowances of moisture and other factors. 



Grade class^ 
ifleation. 



Maximum allowances of- 



Moisture 



Damaged corn. 



Foreign 

material, 

including 

dirt, cob, 

other 

grains, 

finely 

broken 

corn, etc. 



"Cracked" 
corn, not 

including 
finely 
broken 

corn. (See 
general 

rule No. 9.) 



No.l 


Per cent. 
14.0 


No. 2 


15.5 


No. 3 


17.5 


No. 4. 


19.5 


No. 5 


21.5 


No. 6 


23.0 


Sample 





2 per cent (exclusive of heat-damaged or mahogany 
kernels) 

4 per cent (exclusive of heat-damaged or mahogany 
kernels) 

6 per cent (exclusive of heat-damaged or mahogany 
kernels) 

5 per cent (may include heat-damaged or mahogany 
kernels not to exceed one-half of 1 per cent) 

10 per cent (may include heat-damaged or mahogany 
kernels not to exceed 1 per cent) 

15 per cent (may include heat-damaged or mahogany 
kernels not to exceed 3 per cent) 

See general rule No. 6 for sample grade 



GENERAL RULES. 

(1) The corn in grades No. 1 to No. 5, inclusive, must be sweet. 

(2) White corn, all grades, shall be at least 98 per cent white. 

(3) Yellow corn, all grades, shall be at least 95 per cent yellow. 

(4) Mixed corn, all grades, shall include corn of various colors not coming within 
the limits for color as provided for under white or yellow corn. 

71227°— Bull. 168—15 1 



2 BULLETIN 168, U. S. DEPARTMENT OF AGRICULTURE. 

(5) In addition to the various limits indicated, No. 6 corn may be musty, sour, 
and may also include that of inferior quality, such as immature and badly blistered 
corn. 

(6) All corn that does not meet the requirements of either of the six numerical 
grades by reason of an excessive percentage of moisture, damaged kernels, foreign 
matter, or "cracked" corn, or corn that is hot, heat damaged, fire burnt, infested 
with live weevils, or otherwise of distinctly low quality shall be classed as sample 
grade. 

(7) In No. 6 and sample grades, the reasons for so grading shall be stated on the 
inspector's certificate. 

(8) Finely broken corn shall include all broken particles of corn that will pass 
through a metal sieve perforated with round holes nine sixty-fourths of an inch in 
diameter. 

(9) "Cracked" corn shall include all coarsely broken pieces of kernels that will 
pass through a metal sieve perforated with round holes one-quarter of an inch in 
diameter, except that the finely broken corn, as provided for under rule No. 8, shall 
not be considered as "cracked" corn. 

(10) It is understood that the damaged corn, the foreign material (including dirt, 
pieces of cob, finely broken corn, other grains, etc.), and the coarsely broken or 
"cracked" corn, as provided for under the various grades, shall be such as occur 
naturally in corn when handled under good commercial conditions. 

(11) Moisture percentages, as provided for in these grade specifications, shall con- 
form to results obtained by the standard method and tester described in Circular 
No. 72, Bureau of Plant Industry, U. S. Department of Agriculture. 

HOW THE VARIOUS FACTORS SHOULD BE DETERMINED. 

In order that producers, dealers, and consumers throughout the 
United States may fully understand the correct interpretation of 
the Government corn*grades, somewhat detailed explanations are 
given in the following pages. 

In the practical application of these grades it is fully appreciated 
that even with definite limits for the more important factors points 
will arise on which the best of experts may differ. For example, 
there are all degrees of damage and wide variations in color, so that 
some arbitrary line must be drawn as to what shall be considered as 
commercially sound or what shall be considered as white or as yel- 
low. Similar conditions exist on other points. It is believed, how- 
ever, that by the honest adherence to the instructions which follow 
differences in grading will be reduced to a minimum and that the 
grades can be uniformly applied throughout the United States. 

While these explanations are given somewhat in detail and definite 
limits have been fixed for the more important factors, it is not con- 
templated that actual determinations shall be made in the grading 
of every lot of commercial corn. In a large number of cases a com- 
petent and experienced inspector or grader, after he has once become 
familiar with the various limits fixed and established in these 
grades, can estimate the percentage of the various factors with suffi- 
cient accuracy to determine the grade thereof on the basis of his 
judgment. * 

0, GF '2. 

AUG SC'1315 



GRADES FOR COMMERCIAL CORN. 3 

SECURING A REPRESENTATIVE SAMPLE FROM THE BULK. 

In the grading of commercial corn no factor is" of greater importance 
than the securing of a sample representative of the bulk. Likewise, 
no factor is more frequently neglected. In the application of these 
grades to car-lot shipments of corn it is recommended that not less 
^than five probes with a suitable grain trier be taken in such a wa}^ 
X that the composite sample thus secured will represent the average 
of the car as nearly as practicable. On cars not uniformly loaded, 
such additional probes should be made as, in the opinion of the 
sampler, may be necessary to secure a representative sample. In 
cars that show distinct evidence of having been "plugged," and in 
all cases of marked variation in the quality or condition of the corn 
in different parts of the lot being examined, a separate composite 
sample should be taken to represent each such portion. 

If only a part of the grain secured by the various probes is taken 
to a central office for more careful examination and final grading, 
the mixing of the individual sample at the car should receive most 
careful consideration. Very satisfactory results can be secured by 
emptying the contents of the trier each time on a piece of canvas 
and, after all probes have been made, thoroughly mixing the samples 
on the canvas, finally rolling the sample on the canvas, somewhat as 
an expert would roll a cigarette, except that the canvas should be 
held by two opposite sides, which two sides should be securely fas- 
tened to a stick or rod. The larger composite sample can then be 
readily divided into two approximately equal parts by seizing the 
fold of the canvas from beneath with the thumb and index finger; 
then, emptying one portion into the car, the other is retained for the 
office sample. 

Representative samples can not be secured by emptying the con- 
tents of the trier, after each probe, on top of the grain, then roughly 
mixing and taking a portion thereof, usually including a part of the 
surface corn, as a composite sample for the basis of grading. Such 
samples not only fail to represent the bulk, but are misleading, 
especially from the standpoint of dirt and cracked corn. Likewise, 
composite samples made up by emptying only a part of the contents 
of the trier into the can or sample, bag can not, as a rule, be consid- 
ered representative. 

In the sampling of large lots of grain, such as occur in the loading 
of steamers, at least one representative sample made up of a series 
of samples from the various drafts should be taken for each 5,000 
bushels. 

In the sampling of ear corn, where the moisture content is the 
important factor, at least 20 representative ears should be taken at 
random for each 1,000 bushels. In wagon lots of 100 bushels or 



4 BULLETIN 168, IT. S. DEPARTMENT OF AGRICULTURE, 

less, at least 10 representative ears should be selected for test. In 
all ear-corn samples where it is impracticable to shell completely all 
of the selected ears, an approximately equal portion should be 
shelled from the same point or points on each ear. A simple and 
satisfactory method is to break the ears near the middle and then 
shell from the broken ends. In ear corn the damage can usually be 
very closely estimated by classifying a limited number of ears, but 
for a more exact determination it will be necessary to shell the 
selected number of ears completely and determine the percentage of 
damaged kernels in the regular manner. 

MIXING SAMPLES FOR DETAILED ANALYSES. 

Care should be taken to see that the samples used for the detailed 
analyses are representative of the larger sample as drawn from the 
car or other bulk. 

A special sampling or mixing machine for this purpose has been 
developed. This mixing machine will be described in detail in a later 
bulletin of the Department of Agriculture. 

SIZE OF SAMPLES. 

The samples taken from the car or other bulk on which the grading 
is to be based should consist of not less than 1 quart of shelled 
corn. 

The samples for the more detailed analyses, taken from the larger 
sample representing the bulk, should be as follows : 

Moisture content. — 300 grams for each single test. 

Color. — Not less than 100 grams of screened corn. 

"Cracked" corn and foreign material, dirt, etc. — At least 200 grams of the carefully 
mixed sample. In using a 200-gram sample it must be remembered that the weight 
in grams of each of the two factors must be divided by 2 to ascertain the percentage. 

Damaged corn. — Preferably, on the whole of what remains of the sample after remov- 
ing the cracked corn, the foreign material, dirt, etc. In this connection it 
should be remembered that the percentage of damaged corn should be based not on 
the weight of the screened sample but on the weight of the sample taken for analysis 
before removing the cracked corn, the foreign material, dirt, etc. For example, in a 
200-gram sample showing 3 per cent of cracked corn and 2 per cent of foreign mate- 
rial, dirt, etc., there would remain 190 grams to be analyzed for damaged kernels. 
Damaged kernels weighing 20 grams based on the original 200-gram sample would 
therefore be equivalent to 10 per cent, whereas if incorrectly based on only 190 grams 
the percentage of dirt would show as 10.4 per cent. 

SIEVES FOR SCREENING SAMPLES. 

The sieves for screening the samples should be made of metal 
perforated with round holes. The holes in the upper or first sieve 
should be one-quarter of an inch in diameter and the holes in the 
lower or second sieve nine sixty-fourths of an inch in diameter. 
Figures 1 and 2 show these holes of natural size and the approximate 



GRADES FOR COMMERCIAL CORN. 5 

distance from center to center. The thickness of the metal should 
be from 0.025 to 0.035 of an inch. 

Round sieves from 10 to 12 inches in diameter or rectangular sieves 
9 by 11 inches have been found very satisfactory and easy to manipu- 
late. For the most efficient work, the two sieves with the bottom 
pan should be made to nest, so that all screening can be done at one 
operation. 

It is recommended that the sieves be made of brass, aluminum, or 
other suitable metal, pressed from one piece, although sieves made 
by soldering or nailing the perforated metal to any suitable frame 
will give satisfactory results if kept in good repair. 

If made to nest, as shown in figure 3, the depth of the first sieve 
should be 1^ inches, the second 2 inches, and the bottom pan 2 \ inches. 




Fig. 1. — Section of sieve with perforations one- Fig, 2.— Section of sieve with perforations nine 

fourth of an inch in diameter, the distance from sixty-fourtbs of an inch in diameter, the distance 

center to center of holes being approximately from, center to center of holes being approxi- 

eleven thirty-seconds of an inch. ■ mately thirteen sixty-fourths of an. inch. 

If made of metal, at least the bottom pan should be of aluminum, 
to reduce the weight, thereby facilitating the ease of handling. 

MOISTURE TESTS. 

In determining the moisture content, it is desirable that all im- 
portant samples be tested in duplicate whenever practicable and the 
final result based on the average of the two tests. Results of tests 
need not be expressed closer than one-tenth of 1 per cent, and the 
grain should be given the benefit of the doubt in computing aver- 
ages. For example, in taking the average of two tests, one showing 
19.3 per cent and the other 19.4 per cent, the true average would be 
19.35 per cent, but when used in connection with these grades the 
moisture content should be recorded as 19.3 per cent and not 19.35 
per cent. likewise, in single tests any reading in the second decimal 
place may be ignored in moisture determinations. 

Owing to the numerous methods of making moisture determina- 
tions and the wide variations in the results obtained by the different 
methods, the tester and method described in Circular No. 72 of the 



BULLETIN" 168, U. S. DEPAKTMENT OF AGRICULTURE. 



Bureau of Plant Industry, United States Department of Agriculture, 
have been designated as the standard on which the grades have been 
based. Copies of this circular can be secured upon application to 
the United States Department of Agriculture. This in no way pre- 
cludes the use of other methods of making moisture determinations, 
so long as the results are corrected to conform to those secured by 
the standard method specified. Figure 4 represents a sectional view 
of the standard tester that is recommended. The United States 
patent covering this tester has been donated to the people of the 
United States, so that the tester can be used, manufactured, or sold 
by any citizen within the United States without the payment of 
royalty. 

DAMAGED CORN. 

As shown in the grade classification (Table I), the grades 1, 2, and 
3 may contain not to exceed 2, 4, and 6 per cent, respectively, of 

damaged corn, such as "cob-rot- 
ten" corn, "blue eyes/' etc., but 
these first three grades shall not 
include heat-damaged or mahog- 
any kernels. Grades 4, 5, and 6 
may contain not to exceed 8, 10, 
and 15 per cent, respectively, of 
damaged corn, a portion of which 
may consist of heat-damaged or 
mahogany kernels. The heat- 
damaged or mahogany kernels 
permissible as a part of the dam- 
aged corn shall not exceed one- 
half of 1 per cent in No. 4 grade, 1 per cent in No. 5 grade, and 3 per 
cent in No. 6 grade; but the total damaged in these three grades shall 
not exceed 8, 10, and 15 per cent, respectively. 

Types of damaged kernels. — An attempt has been made to show in 
natural colors by means of kernels numbered 1 to 26 in Plate I types 
of kernels which should be classed as damaged. These types of 
damage range from the badly "silk-cut" kernels, shown in No. 1 
(front and back of same kernel), to the very badly "cob-rotten" 
kernels shown in No. 26. These types also include badly shriveled 
kernels which have failed to ripen (shown by kernels numbered 14 
and 15). However, skeleton kernels similar to this type, when con- 
sisting of nothing but the skin of the kernel or of such a character 
that they would be removed by light blowing or fanning, should be 
as foreign material and not as damaged corn. Types of such 
kernels are shown in figure 5. 




Fig.; 



-Nest oi two sieves and bottom pan used in 
grading corn. 



Bui. 168. U. S. Dept. of Agriculture 



Plate I 



TYPES OF COLOR 



1 2 



J ^V' 



4 5 6 






4&f *& ^w -<y 




1 12 13 14 15 16 17 li 



10 



19 20 21 22 23 24 






^itr 







l>> 



25 



26 



27 



TYPES OF DAMAGE 





v 



' J5- 



> 



1 1 



3 4 




1 ^^IP 



i#i 



[0 11 12 



-jj, 
13 



' V ; * % 



14 15 16 17 




&-M& m 






T8 19 20 21 • 22 23 24 25 26 



.sto.ll— 



A.HOEN SCO. BALTIMORE, 



Types of Kernels of Corn for Use in Grading. 



Digitized by the Internet Archive 
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http://www.archive.org/details/gradesforcommercOOduve 



GEADES FOR COMMERCIAL CORN. 



COPN I90"C. 



N?3 RUBBER 

STOPPER 




Fig. 4— Sectional view of standard moisture tester. 



8 BULLETIN 168, IT. S. DEPARTMENT OE AGRICULTUKE. 

Heat-damaged and mahogany kernels. — Corn which has become dis- 
colored as a result of heating due to fermentation or fire damage shall 
be classed as "heat damaged." Badly discolored and darkened 
kernels shall be classed as "mahogany" corn. No heat-damaged 
kernels are shown in the colored plate. 

DETERMINATION OF DAMAGED CORN. 

The percentage of damage should be made on the screened sample, 
preferably by using the entire quantity that remains after removing 
the foreign material and "cracked" corn. In order to simplify the 
determination for damaged corn and to avoid a double penalty, the 
damaged "cracked" corn, as used in these grades, shall be considered 
simply as "cracked" corn; that is, the small quantity of damaged 
"cracked" corn should not be picked out after screening and classified 
as a part of the damaged corn. An excess of damage in the " cracked " 

corn will be evidence of a will- 
ful adulteration and a viola- 
tion of general rule No. 10 of 
the grades. 

FOREIGN MATERIAL. 

The foreign material, in- 
cluding dirt, pieces of cob, 
other grains, finely broken 
corn, etc., as provided for in 
column 4 of Table I, should 

Fig. 5.— Immature skeleton kernels which -vould be include 110 1 Only material that 
removed by Tanning or blowing and should therefore will pass through the sieve 
be classified as foreign material. (Natural size.) \ . . . 

with holes nine sixty-lourths 
of an inch in diameter, as shown in figure 6, but should also in- 
clude the coarser foreign material, such as is shown in figure 7. 
It will be found after a little experience that the coarse material 
shown in figure 7 can be taken out very quickly by hand picking 
after the finer material has been removed by screening, whenever such 
hand picking is necessary to determine correctly the grade of the 
grain in question. 

CRACKED CORN. 

As provided for in general rule No. 9, all coarsely broken pieces of 
kernels that will pass through the metal sieve perforated with round 
holes one-quarter of an inch in diameter (first sieve) and are re- 
tained on the sieve with the smaller perforations (second sieve) 
shall be considered as "cracked" corn, as shown in figure 8. More- 





JF W- ' Ti» , ; ^' ■■«*■- 


§wc 




"0*lJ 







GRADES FOR COMMERCIAL CORN. 




Fig. 0. — Foreign material, including dirt, chaff, other grains, finely 
broken corn, etc., which will pass through the sieve with the smaller 
perforations, nine sixty-fourths of an inch in diameter. (Natural 
size.) 



over this is the only broken corn which should be so classified in 
these grades. The finely broken pieces which will pass through the 
sieve with the smaller perforations should be classed with the for- 
eign material, and the large pieces which remain on the sieve with 
the quarter-inch holes 
should be classed with 
the whole kernels. 

However, it is not 
intended that all ma- 
terial remaining on 
the -sieve with the 
smaller holes shall be 
classed as ' c cracked ' ; 
corn. All small whole 
kernels, such as those 
that are shown in 
figure 9, which will 
go through the sieve 
with the quarter-inch 
holes should be picked 
out after screening and classed as whole corn. Likewise, any "other 
grains/' pieces of cob, or other foreign material remaining with the 
"cracked" corn on the sieve with the smaller holes should be picked 
out and added to the foreign material, dirt, etc. In applying these 

grades, no separation 
should be made of 
the sound and the 
damaged "cracked" 
corn, but the whole 
should be classed only 
as "cracked" corn. 

COLOR. 

Color determina- 
tions should be made 
on not less than 100 
grams of the screened 
sample; that is, after 
the "cracked" corn 
and foreign material 
have been removed. All grades of white corn require that at least 
98 per cent, by weight, shall be white, as stated in general rule 
No. 2, and all grades of yellow corn require that at least 95 per 
cent shall be yellow, as provided in general rule No. 3. In most 




Fig. 7.— Coarse material, which will not pass through the sieve with 
the smaller perforations, nine sixty-fourths of an inch in diameter, 
but which should be picked out of the sample and included with the 
foreign material, dirt, cob, other grains, etc. (Natural size.) 



10 



BULLETIN 168, U. S. DEPARTMENT OF AGRICULTURE. 



cases, when exainining white corn it will not be necessary to make 
weighings unless there are more than 5 kernels of corn of other 
colors, and on yellow corn, unless there are more than 12 kernels of 




Fig. 8. — "Cracked" corn, consisting of piece? of kernels which v. ill pass through the sieve with the 
quarter-inch perforations. (Natural size.) 

other colors, in a 100-gram sample, as 5 kernels will usually be less 
than 2 per cent and 12 kernels less than 5 per cent. 

More difficult problems arise, however, in dealing with special 
types or varieties of corn or with individual kernels, such as "straw- 




Fig. 9.— Small whole kernels which will pass through the. sieve with the quarter-inch perforations, 
but which should not be classed as ''cracked" corn. (Natural size.) 

colored/' "red-cast" yellow, etc., which are difficult to classify. At 
most, such classifications can be only arbitrary and in keeping with 
the best commercial practices. In order to bring about the greatest 
uniformity of application, some of the more important types of ker- 
nels from the standpoint of color are shown in Plate I in natural 



GRADES FOE COMMERCIAL CORN. 11 

colors, as nearly as it is possible to reproduce them. Kernels num- 
bered 1 to 9, inclusive, under types of color, have been classified as 
white corn. It will be noted that some of the kernels at the right in 
this first series: are of a very light straw color, but not sufficient to 
justify their being classed as of other colors when found in a grade 
of white corn. Kernels with a tinge of pink over white (not shown 
in the plate) should be considered on the same basis as straw-colored 
kernels; that is, where the pink color is only very slight they may be 
classed as white; otherwise they should be eliminated. In kernel 
No. 10, however, the yellow color is more pronounced, and such ker- 
nels should not be classed as either white or yellow corn. The same 
is true with all kernels numbered 10 to 18, inclusive. Kernels num- 
bered 10 to 14, inclusive, are intended to represent white-capped 
pale yellow, kernel No. 19 represents a pale yellow of the lowest 
type, and kernel No. 27 represents a "red-cast" yellow of the most 
pronounced type which should be classed as yellow corn. 



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